UF 

575 

F8 

75  mm 
E5 


UC-NRLF 

III 

$B   313   234 


NT 
CD 


M 


Jut  19  1918 


NOTES 


ON  THE 


FRENCH  75-MM.  GU 


EDITED  AT  THE  ARMY  WAR  COLLEGE 
OCTOBER,  1917 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1917 


War  Department. 

Document  No.  687. 

Office  0/  The  Adjutant  General, 


WAR  DEPARTIMENT, 

Washington,  October  22,  1917. 
The  following  pamphlet  "  Notes  on  the  French  75-mm.  Gun," 
reprint  from  an  article  in  "The  Engineer"  (London),  January 
22,  1915,  is  published  for  the  information  of  all  concerned. 
[062.1  A.  G.  O.] 

By  ordek  of  the  Secbetary  of  War: 

TASKER  H.  BLISS. 

General,  Chief  of  Staff. 
Official  : 

H.  P.  McCAIN, 

.   The  Adjutant  General. 

21868°— 17  (3) 


.377770 


THE  FRENCH  75-MM.  GUN. 


With  the  exception  of  the  German  "  42,"  no  gun  in  the  war 
has  created  more  interest  than  the  famous  French  75-mra. 
field  gun,  popularly  known  as  the  soixante-quinze.  That  it 
did  magnificent  work  in  the  early  stages  of  the  war  can  not 
be  doubted,  and  if  its  influence  is  at  present  not  so  great  as  it 
was,  the  reason  is  to  be  found  in  the  siege  conditions  that  pre- 
vail and  to  the  momentary  need  of  heavier  pieces.  We  do  not 
doubt,  however,  that  the  "  75  "  will  come  by  its  own  again  soon, 
when  this  interminable  trench  war  reaches  an  end  and  more 
rapid  movements  begin. 

It  will  surprise  many  of  our  readers  to  learn  that  the 
"  soixante-quinze "  is  not  a  new  gun.  It  was  invented  as  far 
back  as  1897,  and  two  such  famous  artillerists  as  Deport  and 
Sainte-Claire  Deville  had  a  hand  in  its  design.  Studying  it  in 
detail,  as  we  are  now  able  to  do,  through  an  admirable  article 
recently  written  by  M.  Dumas  for  Le  G^nie  Civil,  we  are  struck 
by  the  excellence  of  the  design.  In  all  respects  it  is  far  ahead 
of  any  gun  not  only  of  its  time  but  of  later  years.  It  represents 
the  first  real  attempt  to  produce  a  fieldpiece  that  could  quite 
correctly  be  called  a  quick  firer,  and  it  was  probably  the  earliest 
in  which  independent  recoil  was  combined  with  independent 
training,  a  quick-action  breech  mechanism,  and  fixed  loading — 
that  is  to  say,  loading  in  which  the  projectile  and  the  charge  are 
united  in  a  single  cartridge,  just  as  they  are  in  the  charge  of  a 
rifle. 

The  gun  proper  consists  of  a  barrel  rifled  with  cuneiform 
grooves  and  strengthened  by  a  breech  hoop  pressed  on  cold ;  its 
bore  is  75  mm. — practically  3-inch — and  its  length  is  2.475  m., 
or  33  calibers.  The  breech  is  not  closed  by  a  block  with  an 
interrupted  thread,  nor  by  a  sliding  block,  as  in  most  other  guns, 
but  by  a  revolving  block,  the  axis  of  which  does  not  coincide 
with  the  axis  of  the  gun.  At  one  place  a  deep  notch  is  cut  into 
this  block,  which,  in  a  certain  position,  coincides  with  the  bore 
of  the  gun  and  permits  the  cartridge  to  be  pushed  in.  By  giving 
half  a  revolution  to  the  block  the  notch  is  moved  out  of  the  way 
and  the  breech  is  closed  by  the  solid  part.    The  block  is  screwed 

(5) 


6; 


on  the  outside,  so  that  not  only  is  it  strongly  supported  against 
the  pressure  of  explosion,  but  presses  the  rim  of  the  cartridge 
hard  up  against  the  gun  face  in  the  closed  position.  It  is  turned 
from  one  position  to  another  by  a  lever  projecting  on  top,  as 
shown  in  Fig.  1.  In  the  lever  is  a  grip  bolt,  which  locks  it  in 
either  the  closed  or  open  position.  In  Fig.  1  are  also  seen  the  two 
arms  which  extract  the  cartridge  case  and  automatically  throw 
it  to  the  rear  when  the  breech  is  opened.    They  are  operated  by  a 


xtractor 


Fig.  1. — Breechblock. 


short  lever  or  heel  which  engages  in  a  fixed  groove  or  cam.  Fir- 
ing is  effected  by  a  spring  trigger  acting  on  a  striker  which  passes 
right  through  the  block.  A  safety  cam  is  provided  to  hold  the 
trigger  out  of  action  when  desired. 

The  details  of  the  recoil  cylinder  can  not,  according  to  Lg 
G^nie  Civil,  yet  be  published,  but  from  the  sketch  given  and 
here  reproduced^fig.  2 — it  is  clear  that  the  form  is  one  now 
fairly  well  known.  The  recoil  cylinder,  which  is  a  brake  and 
running-out  gear  combined,  is  supported  in  a  cradle  carried  by 


Fig.  2. — Recoil  cylinder. 

trunnions  on  the  gun  carriage.  It  consists  of  two  parts,  the 
cylinder  C  and  the  cylinder  R.  The  former  of  these,  C,  is  at- 
tached rigidly  to  a  projection  L  on  the  breech  of  the  gun,  and 
when  the  gun  recoils — toward  the  left — this  cylinder  is  drawn 
back  with  it.  The  other  cylinder  R  is  attached  to  the  cradle 
and  remains  at  rest.  In  it  is  a  diaphragm  or  piston  D.  Solid 
with  R  is  a  hollow  piston  rod  provided  with  a  piston  which  fits 
the  cylinder  C.  The  end  of  the  hole  in  the  rod  is  closed  by  a 
spring-loaded  valve  S,  beside  which,  through  small  holes  pro- 


vided  for  the  purpose,  some  leakage  is  permitted.  The  whole 
space  to  the  left  of  the  piston  D  is  filled  with  a  nonfreezing  mix- 
ture of  glycerin  and  water.  On  the  right  of  D  there  is  air. 
When  the  gun  is  fired  the  cylinder  C  is  drawn  to  the  left  and 
the  glycerin  and  water  is  forced,  following  the  arrows,  through 
the  valve  S,  driving  back  the  piston  D  and  compressing  the  air 
behind  it.  The  smallness  of  the  passages,  the  pressure  of  the 
loaded  valve  S,  and  the  resistance  of  the  air  to  compression 
cause  this  action  to  take  place  quietly  and  bring  the  gun  to  rest 
at  the  end  of  about  1  m.  20  cm.,  say  4  feet.  The  compressed  air 
then  expands  again,  drives  the  liquid  back  into  the  cylinder  C, 
and  returns  the  gun  to  the  firing  position. 


\  \Wheel 


.       \PivoUed   — . 
.i      I. 

in   hi 


Fig.  3. — Wheel-brake  gear. 

It  is  claimed  for  the  carriage  of  the  "  soixante-quinze  "  that 
it  has  three  essential  points  of  difference  from  any  carriage 
that  preceded  it.  They  are;  (1)  The  combination  of  a  trail- 
spade  with  wheel  brakes;  (2)  the  possibility  of  training  the 
gun  without  moving  the  wheels;  and  (3)  a  mechanism  which 
permits  aim  to  be  taken  during  recoil.  We  shall  take  them  in 
the  order  given.  In  the  firing  position  the  carriage  rests  on 
three  points,  namely,  the  end  of 'the  trail  and  the  two  brake 
blocks,  which  are  forced  under  the  wheel.  All  three  have 
spades,  so  that  they  attach  themselves  firmly  to  the  ground. 
The  wheels,  it  will  be  seen,  are  entirely  out  of  action  and  the  car- 
riage is  borne  by  a  three-point  suspension,  which,  as  everyone 
knows,  is  ideally  the  best  possible.  The  method  of  raising  the 
wheels  onto  the  shoes  is  shown  diagi*ammatically  in  Fig.  3. 
Each  shoe  is  attached  to  the  extremity  of  a  radius  rod  centered 


8 

on  the  axle,  and  the  two  rods  are  connected  together  by  a  cross 
piece,  and  to  the  trail  by  rods  represented  by  O  T.  On  the 
under  side  of  the  trail  is  fixed  a  rack,  shown  in  the  plan  view, 
Fig.  3.  When  the  gun  is  to  be  brought  into  action  the  trail 
is  raised  as  shown  dotted,  and  the  end  O  of  the  rod  O  T  slides 
along  the  rack  to  the  point  T\  On  lowering  the  trail  O  engages 
with  the  rack  and  prevents  E  P  from  closing  up  on  the  trail, 
with  the  consequence  that  as  the  latter  descends  rotation  takes 
place  about  P  and  the  wheel  mounts  the  shoe. 

Having  got  the  carriage  into  position  with  the  gun  pointing 
as  nearly  as  possible  in  the  right  direction  training  is  effected 
by  lateral  movement  of  the  gun,  not  about  a  point  on  the  axle 
as  center  of  rotation,  but  about  the  trail  spade  as  center  of  rota- 
tion. This  is  a  very  important  point,  because  it  results  in  the 
thrust  of  the  recoil  always  being  carried  in  a  straight  line 


Fig.  4. 


through  the  trail  and  there  is  very  little  tendency  to  throw  off 
sideways.  The  desired  movement  is  effected  by  cutting  a  screw 
on  the  central  portion  of  the  axle  and  fitting  it  with  a  nut  which 
can  be  rotated  by  a  handwheel.  The  nut  is  suitably  attached 
to  the  upper  end  of  the  trail  and  consequently  carries  the  latter 
with  it.  It  follows  from  this  movement  that  one  wheel  tends 
to  go  back  and  the  other  forward  in  the  endeavor  of  the  axle  to 
remain  normal  to  the  trail,  and  the  arrangement  of  the  rods  seen 
in  the  plan  view  of  Fig.  3  permits  this  small  displacement  to 
take  place. 

Turning  now  to  the  aiming  mechanism,  we  direct  attention  to 
Fig.  4.  Suppose  a  gun  placed  at  P  and  desiring  to  strike  a  tar- 
get at  O.  It  must  obviously  be  given  an  upward  inclination 
equal  to  S+T,  S  being  the  angle  which  makes  it  point  direct  at 
O  and  T  the  angle  necessitated  by  the  curved  trajectory  of  the 
projectile.  It  is  desired  to  make  the  adjustment  of  these  two 
angles  independent  of  each  other.  How  this  is  affected  will 
be  gathered  readily  from  Fig.  5,  which  is  purely  diagrammatic. 


9 

Centered  on  the  trunnions  of  the  gun  cradle  is  a  pair  of  arms 
B  fitted  with  toothed  sectors  D.  A  pinion  R  rotated  by  a  hand- 
wheel  on  the  left  side  of  the  trail  moves  the  rack.  A  spirit  level 
coupled  to  this  apparatus  is  placed  in  front  of  the  operator, 
whose  whole  business  is  to  keep  the  bubble  in  the  center.  The 
effect  on  perfectly  level  ground  and  with  the  gun  at  no  degrees 
elevation  would  be  absolutely  horizontal  fire.  On  uneven  ground 
the  effect  is  to  bring  the  gun  back  to  level  and  so  provide  a  fixed 
datum  for  the  adustment  of  the#  angle  of  elevation.  On  the 
right  side  of  the  trail  is  another  handwheel,  which  turns  the  nut 
M  upon  the  fixed  screw  V.  The  nut  is  coupled  to  the  rear  end 
of  the  cradle,  and  as  it  rises  or  falls  it  raises  or  depresses  the 
muzzle  relatively  to  the  horizontal.     One  member  of  the  gun 


Fig.  5. — Elevating  gear. 

cTew  looks  after  one  handwheel  and  another  looks  after  the 
other,  and  the  two  work  quite  independently,  the  one  always 
maintaining  the  angle  S  of  the  piece  while  the  other  gives  the 
necessary  elevation.  The  procedure  probably  is  to  put  the  ele- 
vating gear  at  zero,  angle  T  =  0,  and  then  direct  the  gun  point 
blank  at  the  target  by  turning  the  pinion  R.  This  will  incline 
the  level,  which  must  be  again  brought  back  to  the  horizontal 
and  fastened  in  that  position.  The  necessary  degrees  of  eleva- 
tion are  then  fixed  on  the  graduated  quadrant  H,  or  rather  on 
its  equivalent,  a  drum  which  gives  a  magnified  reading. 

Its  ammunition  wagon  is  almost  as  interesting  as  the 
"  soixante-quinze "  itself.  A  perspective  drawing  is  given  in 
'Fig.  6.  It  consists  of  two  compartments  separated  by  a  locker 
and  space  for  a  fuze-setting  appliance.  It  is  shown  in  Fig.  6 
in  position  for  use  with  the  covers  open  as  shields  for  the  men 
behind.    On  the  road  the  covers  are  closed  and  the  wagon  is 


10 

returned  to  the  horizontal  with  the  projectiles  resting  point 
downward.  The  fuze-timing  appliance  was  one  of  the  innova- 
tions introduced  with  the  "  soixante-quinze  "  and  is  known  as  the 
Mhouchoir,  the  "  uncorker  " — Fig.  7.  It  consists  of  a  plate  with 
two  depressions  O  formed  to  the  ogive  of  the  projectile,  a  handle 
M  passing  over  a  dial  marked  in  distances  and  two  levers  L 
actuating  two  punches  P.  The  distance  at  which  the  shell  is 
desired  to  burst  is  set  on  the  dial  and  each  shell,  as  it  is  taken 
out  of  the  caisson,  is  held  no^e  downward  in  one  of  the  recesses. 
Pressure  is  then  put  upon  the  lever.  By  this  means  the  fuze  is 
set  very  rapidly. 


Fig.  6. — Ammunition  wagon. 


To  understand  more  fully  what  happens  we  must  look  at  the 
fuze  itself — see  Fig.  8 — which  again  is  diagrammatic.  Inside 
the  body  piece  is  a  conical  chamber  containing  a  hammer  M 
pressed  to  the  front  by  a  light  spring  r.  At  c  is  a  detonating 
cap  and  at  X  a  block  of  compressed  powder.  Outside  the  cone 
is  a  spiral  groove  filled  with  fuze  mixture  communicating  with 
a  chamber  below,  which  is  open  to  the  explosive  charge  inside 
the  shell.  When  the  gun  is  fired  the  inertia  of  M  causes  it  to 
compress  the  spring  V  and  strike  the  detonator  c;  this  ignites 
X,  the  flame  from  which  passes  through  a  hole  Y  pierced  by  the 
"  uncorker."  The  fuze  mixture  then  takes  fire,  burns  round  the 
spiral,  reaches  the  interior,  and  explodes  the  bursting  charge. 
It  will  be  seen  that  the  shorter  the  length  of  fuze  mixture  from 


11 


the  hole  pierced  by  the  d^houchoir  to  the  interior  the  earlier  is 
tlie  burst,  and  vice  versa.  Hence  by  piercing  tlie  hole  at  different 
points  the  time  of  bursting  can  be  adjusted.  We  gather  that 
with  this  fuze  there  is  no  timing  scale  as  in  our  own  and  Ger- 
man shell.  This  is  a  feature  of  some  value,  for  if  the  nose  of  a 
German  shell  be  picked  up  the  distance  from  which  it  has  been 
fireil  may  be  estimated  by  examination  of  the  scale  on  the  fuze. 

The  fuze  shown  in  figure  8  is  also  percussive — that  is  to  say, 
if  it  fails  to  explode  either  accidentally  or  intentionally  in  the 


Fig.  7. — Fuze  setter. 


Fig.   8. 


-Time   and   percus- 
sion fuze. 


air  it  bursts  on  impact  with  the  ground  or  other  obstacle.  The 
essential  parts  are  the  fuze  tube  B  held  downward  by  the 
spring  R  and  provided  at  its  point  with  the  detonating  cap  A; 
and  the  sleeve  m  fitted  inside  with  pawls  G.  The  striker  S  is 
fixed  to  the  body  of  the  fuze.  When  the  gun  is  fired  the  sleeve 
m,  by  its  inertia,  compresses  the  spring  R  and  the  pawls  engage 
with  the  serrations  on  the  outside  of  the  fuze  tube  B.  The 
spring  is  thus  held  in  compression  and  m,  R,  and  B  move  as  one 
piece.  On  impact  their  momentum  carries  them  forward,  com- 
pressing the  light  spring  R\  and  drives  the^tap  A  against  the 
striker  S. 


12 

When  using  the  explosive  shell,  which,  while  weighing  less 
than  the  shrapnel — 5.3  kilos,  as  against  7.2  kilos — ^appears  to  be 
very  destructive,  a  delaying  fuze  is  used.  It  contains  a  slow- 
burning  mixture,  which  is  ignited  by  the  impact  fuze,  and  in  its 
turn  fires  a  charge  of  melinite,  which  explodes  the  shell.  The 
object  is  to  allow  the  shell  to  enter  the  target  some  distance 
before  bursting,  the  effects  being  more  pronounced  than  when 
the  explosion  takes  place  on  the  surface. 

The  range  of  the  '*  soixante-quinze  "  Is  6,500  meters — nearly 
4  miles — the  projectile,  shrapnel,  weighs  7.2  kilos,  and  the  charge 
0.7  kilo.  The  muzzle  velocity  is  529  meter-seconds ;  the  velocity 
at  1,000  meters,  413  meter-seconds ;  at  2,000,  334  meter-seconds ; 
and  at  3,000,  290  meter-seconds.  The  shrapnel  contains  300 
balls  weighing  12  grams  each.  The  weight  of  the  piece  ready 
for  action  is  1,100  kilos,  and  of  the  ammunition  wagon,  with 
72  rounds,  1,950  kilos. 

o 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 

RENEWALS  ONLY— TEL.  NO.  642^405 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 

Renewed  books  are  subject  to  immediate  recall. 

JAN  14  1969  2  8 

i 

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j\VtTO0isC.W»28'88 

AUG  12  1990 

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T  T^  oi  A    OQ     c  .«Q                             General  Library 

